Herpesvirus infections cause serious morbidity and can be fatal after hematopoietic cell transplantation (HCT). The goal of Project 8 is to explore the hypothesis that early reconstitution of innate antiviral immunity acts in concert with adaptive immunity to control these infections. Specific Aim 1 will assess relationships between reconstitution of natural killer (NK) cells and varicella-zoster virus (VZV)- specific and cytomegalovirus (CMV)-specific T cells and VZV and CMV reactivation. Allogeneic HCT patients will be evaluated at 30 and 90 days and 6 and 12 months after HCT using flow cytometry methods to assess NK cell maturity, receptor repertoire and T cell-dependent IFN^y production and for virus-specific CD4 and CDS T cell frequencies. To establish correlations with protection, patients will be monitored for clinical VZV and CMV disease and subclinical infections, detected by PCR testing of peripheral blood mononuclear cells for viremia. Statistical analyses of relationships among measures of immune reconstitution, viral infection and clinical variables will be done. In Specific Aim 2, we will evaluate innate control of VZV infection in dorsal root ganglia (DRG) xenografts in the SCIDhu mouse model. Innate responses will be investigated using immunohistochemistry to assess interferon (IFN) and Nuclear Factor K-B (NFicB) up-regulation and interleukin-15 (IL-15) expression in VZV-infected and uninfected neurons and non-neuronal cells. Modulation of VZV infection by exogenous IFN-a, IFN-y or IL-15 will be determined by infecting DRG with VZV rOkaF62/63RL, which has a firefly luciferase reporter cassette allowing non-invasive assessment of VZV replication. Whether adoptive transfer of NK cells or cytokine-induced killer cells limits VZV replication in DRG will also be investigated. The SCIDhu DRG model offers a unique opportunity to assess the antiviral effects of cytokines and cellular immunotherapy on VZV replication in sensory ganglia in vivo and should demonstrate whether innate responses can restrict VZV replication in a system that mimics allogeneic HCT. Profiling innate and adaptive immune responses in HCT patients along with surveillance for VZV and CMV reactivation and disease will identify antiviral mechanisms that are important for modifying herpesvirus infections after HCT. Exogenous IFNs and IL-15 are modalities that can be considered as adjunctive therapies in HCT recipients. Adoptive cell therapies, including CIK cells are being evaluated for tumoricidal activity in HCT recipients and could have the incremental benefit of controlling herpesvirus infections. These prospective clinical studies of innate and adaptive immunity to VZV and CMV and experiments in VZV- infected SCIDhu DRG have the potential to yield new insights about antiviral immune mechanisms and to suggest new measures for minimizing the burden of herpesvirus-related disease after HCT.